Monitoring of soil microbial inoculants and their impact on maize (Zea mays L.) rhizosphere using T-RFLP molecular fingerprint method

Abstract

Plant Growth Promoting Rhizobacteria (PGPR) are commonly applied in agricultural systems as biofertilizers due to their beneficial effects on plant productivity and crop yield. Considering the growing nutritional needs of the human population, PGPR inoculants adapted to deteriorated soil conditions offer a sustainable way for crop production. The objective of this study was to detect the presence and estimate the relative abundance of the PGPR members of ‘stress-tolerant’ bacterial inocula, and to investigate their effect on the indigenous bacterial community structure of the maize rhizosphere. The acid stress tolerant bacterial inocula were compared to inocula used in mildly alkaline soil, during the 112-day growth period of maize. The Terminal Restriction Fragment Length Polymorphism (T-RFLP) molecular fingerprint method offered a possibility for monitoring the applied bacteria. Two different restriction endonucleases were selected in silico and tested in vitro for specific detection of the inoculated PGPR. The developed T-RFLP model system indicated a clear positive effect of inoculants on the relative abundance of Azospirillum species in mildly alkaline (pH 7.3) and acid (pH 5.35) plot between days 14 and 21, and also on that of Agreia pratensis in acid plot in the period between days 35 and 56. In case of Azospirillum and acid soil the positive effect proved to be statistically significant (2–5 times higher relative abundances compared to the control). Similarly, the abundances of the monitored PGPR species and the maize yield were more positively influenced in acid soil than in mildly alkaline soil treated by the inocula developed. In the case of acid soil treatments resulted in significant growth of cob number (1.29–1.44 times of the control). The bacterial community structure of the rhizosphere significantly differed depending on soil type and maize growth stage.